Magnetic data storage devices



July 12, 1960 Filed Nov. 7, 1958 R. D. FISHER EI'AL MAGNETIC DATA STORAGE DEVICES 5 Sheets-Sheet 1 INVENTORS ROBERT D. FISHER JEROME S. SALLO 6 IGNM'IU U (1 M THEIR ATTORNEYS y 1960 R. D. FISHER ETAL 2,945,217

MAGNETIC DATA STORAGE DEVICES Filed Nov. 7, 1958 5 Sheets-Sheet 2 INVENTORS ROBERT D. FISHER JEROME S. SALLO 8 IGNATIUS TSU THEIR ATTORNEYS July 12, 196 R. D. FISHER ETAL 2,945,217

MAGNETIC DATA STORAGE DEVICES Filed Nov. 7, 1958 5 Sheets-Sheet 3 FIG. 3

mvsmons l6 ROBERT D. FISHER JEROME s. SALLO a mumus Tsu THEIR ATTORNEYS y 1960 R. o. FISHER ETAL 2,945,217

' MAGNETIC DATA STORAGE DEVICES Filed Nov. 7, 195a s Sheets-Sheet 4 7 FIG. 4

. INVENTORS l6 ROBERT D. FISHER JEROME S. SALLO 8 IGNATIUS TSU BY M THEIR ATTORNEYS July 12, 1960 Filed Nov. 7, 1958 R. D. FlSHER ET AL MAGNETIC DATA STORAGE DEVICES 5 Sheets-Sheet 5 INVENTORS ROBERT D. FISHER JEROME S. SALLO 8a IGNATIUS TSU THEIR ATTORNEYS United States Patent MAGNETIC DATA STORAGE DEVICES Robert D. Fisher, Jerome .s. Sallo, and Ignatius Tsu, Dayton, Ohio, assignors to The National Cash Register Company, Dayton, Ohio, a corporation of Maryland Filed Nov. 7, 1958, Ser. No. 827,412

13 Claims. (Cl. 340-174 The present invention relates generally to data storage devices and more specifically relates to new and improved magnetic data storage devices which are adaptable for use as memory elements in present day electronic computers and data processors.

.Magnetic data storage devices presently employed in a coincident current memory, are normally in the form of magnetic cores of toroidal configuration and have a relatively high magnetic remanence and a substantially rectangular hysteresis characteristic. However, even though toroidal cores are admirably well suited as storage devices, they are nevertheless extremely fragile, quite diflicult to fabricate, and require an expenditure of a considerable amount of time and effort in order to be operatively connected in circuit. 1

In an attempt to alleviate some of these problems, ther has been developed a magnetic data storage device commonly known as a twistor, such as shown and described in the November 1957 issue of The Bell System Technical Journal by A. H. Bobeck, volume XXXVI, pages 1319 to 1340. .Such a device normally comprises a length of non-magnetic electrically conductive wire, which constitutes a common core, and a coaxial layer of saturable ferromagnetic material extruded on the outermost surface of the core. The core and the ferromagnetic coating are both simultaneously stretched and twisted and the ends thereof maintained in a fixed position during operation of the device. As a direct result of the applied stretching and twisting actions, the easy direction of magnetization of'the magnetic coating is orient ed from a direction substantially parallel to the longitudii coincident. half-select currents is at least equal in magmtude to (:H) oersteds and is oriented in the same di-,

ice

During reading of a selected length portion of the coating, either the core or the corresponding coil is pulsed nal axis of the core to a coaxial one of substantially of twist, are allowed to attain one or the other of two stable conditions, respectively characterized by a.,positive or negative magnetic remanence- Thus, a magnetic field of (:H) oersteds, along the direction oftwist, switches the length-portions from one state to another, whereas 'a field of -H/ 2) oersteds produces only negliflgible changes in the magneticremanence of the coating.

During operation of the device, a plurality of similar coils are separately wound thereabout and are positioned in a spaced sideeby-side relationship with respect to one another to encompass and thereby define a correspond- .ing plurality of helical-path length portions of ferromagnetic material. Storage of binary information in a select- ..ed length portion of the coating is accomplished by sendving a current impulse of half-select magnitude into the conductive wire of the common core and simultaneously sending a current impulse of half-select magnitude into the selected coil in such directions that the vector sum;

.-;mation. of the magnetic ,fields produced by both of the with a current impulse of full-select magnitude to in:

dividually develop a magnetic field of at least :H- oersteds in the opposite direction from the magnetic field developed during storage of the function. In response to the read impulse, an electrical signal is or is not available between the ends of the core, or the corresponding coil, depending upon which one was pulsed, according to whether the binary information (1) or (0) had previously been established in that particular length portion of the coating encompassed by that particular coil,

as represented by its positive remanence.

However, with reference to copending application 696,987, of J. R. Anderson et al., for Magnetic Data Storage Devices, filed November 18, 1957, and assigned to the present assignee, there is shown and described a method of fabricating a so-called pre-twisted! twistor which does not require the ends thereof to be fixedly secured during operation of the device. In such a fabrication process, an elongated substrate of electrically conductive material is first twisted relative to a longitudi nal axis thereof. Thereafter, a ferromagnetic coating is electrodeposited on the outermost surface thereof, after which time the ends thereof are released and the coated substrate is allowed to approach its original state as before being twisted. As a result of the release, a torsional strain is stored in the ferromagnetic coating which is related to, but opposite in direction from, the mechani: cally applied stress stored in the substrate prior to deposition of the coating thereon. Consequently, the easy direction of magnetization of the ferromagnetic material is oriented in a helical direction with respect to the longitudinal axis of the substrate as before, but without the necessity of an external torsional strain being applied to the ends thereof after fabrication.

Even though such a pre-twisted magentic data storage device possesses many improved magnetic and other desirable features with respect to those previously fab ricated, it is nevertheless highly desirable to completely eliminate the necessity for the application thereto of an external mechanically generated torsional strain either before, during, or after fabrication of the device.

Therefore, one of'the primary objects of the present invention is to devise a new and improved magnetic data storage device which possesses ali of the advantages of prior twistor type storage devices but does not necessitate the application of a mechanically generated torsion al strain either before, during, or after fabrication thereof.

Another object of the present invention is to devise a unique magnetic data storage device which character istically possesses a direction of magnetization which is skewed with respect to a longitudinal axis thereof and yet is substantially free from mechanically imparted torsional ,strain.

Still another object of the present invention is to devise such a magnetic data storage device having greatly improved ,magnetic and other characteristics than heretofore possible.

A corollary object of the present invention is to devise such a magnetic data storage device which is capable of being economically fabricated by mass production techniques and is readily adaptable for incorporation as a memory element in present-day electronic computers and data processors.

or negative magnetic Patented July 12,1960

' bronze, etc.

In accordance with the present invention, such a new and improved magnetic data device comprises an elongated electrically conductive substrate having a ferromagnetic electrodeposit disposed on the surface thereof. The electrodeposit has the characteristics of being substantially free from mechanically imparted torsional strain and having a skewed easy direction of magnetization with respect to the longitudinal axis of the substrate.

' However, the novel features ofthe present invention, as well as the invention itself, both as to its structural organization and as to its mode of operation, will be more readily and completely understood from the following detailed description when considered in connection with the accompanying drawings, in which like reference numerals refer to like or similar elements, and in which:

'Fig. 1 is an electron micrograph of the surface of a prior non-twisted plated twistor type of magnetic data storage device, magnification 16,500X;

Fig. 2 is an electron micrograph of the surface of a magnetic data storage device in accordance with the present invention, magnification 16,500X;

Fig. 3 is an X-ray diffraction pattern of the same non twisted plated twistor type of magnetic data storage device as shown in Fig. 1; V

Fig. 4 is an X-ray diffraction pattern of the magnetic data storage device in accordance with the present invention as shown in Fig. 3; and

Figs. 5 and 6 illustrate modes of operation of the novel magnetic data storage devices of the present invention.

In the preferred electrodeposition process of fabricating the unique magnetic data storage devices of the present invention, an aqueous electrolytic bath is first prepared having preferred constituent concentrations in ac cordance with either of the exemplary plating baths #1, #2, or #3 which are listed below in chart form and in which chart the concentration of each constituent is given in grams per liter of aqueous solution.

Plating Bath Constituents Con0(cn/t1r)ation Bath Bath Bath Ferric chloride (FeChfiHrO) 8 13 8 Ferrous chloride (FeClzAHzO)... 12 Nickel chloride (NiClrfiH OL 20 Ammonium chloride (NI-I401) 50 50 50 Sodium Molybdate (NaflViOOt E120). 1 Sodium Citrate (NaQCttH5OL2H20) 126 Ammonium Citrate (N H I-ICuI-I O1.2H 0 40 40 After an electrolytic bath has been prepared having constituent concentrations as shown by either #1, #2, or #3, the pH of the bath is adjusted to approximately 8.5 by the addition thereto of a suitable amount of ammonium hydroxide (NI-1 0E). Even though the bath may be successfully operated at ordinary room temperature, the temperature thereof, nevertheless, is preferably adjusted to approximately 90 degrees centigrade. Thereafter, the bath is introduced into a conventional rubberlined steel plating tank, or an equivalent inert plastic container. The substrate (illustrated as 20 in Figs. 5 and 6), onto which the electrodeposit 21 is to be formed, may be composed of any of a variety of electrically conductive materials such as alloys of copper, aluminum, brass, The physical shape of the substrate is not critical and may even be an extremely thin electrically conductive film which is mechanically supported by an insulating material such as glass, plastic, ceramic, or the like. For some applications, it is preferred that the sub strate be in the form of a Phosphor-bronze wire having a diameter of approximately 9 mils. However, due to the fact that undesired strains tend to alter the magnetic properties of the deposit, it is generally necessary to packagethe devices. This problem is diminished, however, by depositing the ferromagnetic coating onto a tubular or hollow substrate, as illustrated in Fig. 6, since a tube 4 is more rigid than a solid substrate of the same diameter. The tubular structure offers added advantages in that additional sense, drive and/or inhibit windings may be conveniently threaded therethrough in the manner as illustrated by 22 in Fig. 6. In either event, it is of course necessary that the metallic substrate, whether hollow (Fig. 6) or otherwise (Fig. 5), be cleaned in a conventional manner before plating, through the use of any of the well known alkaline-acid-water methods as used by present-day plating industries.

As in the previously described twistor type of magnetic data storage device as further described in the aforementioned copcnding application Serial No. 696,987, it is desirable to secure a relatively thin ferromagnetic deposit on the substrate having a thickness in the order of one ten-thousandths of an inch so as to maintain eddy current losses therein at a minimum and yet be thick enough to insure adequate readout voltage during operation of the device as a memory element. Consequently, it is necessary that the substrate be exposed as a cathode to electrolytic action in the bath for only a short period of time, preferably in the order of 1 minute, depending upon of course the particular value of cathode current density chosen to be used in the plating process. To accomplish this, the process is made a continuous one whereby the wire substrate is moved through the bath at a constant speed, by any well known means, with electrical contact at all times being maintained with the substrate to supply the plating current thereto. It is also preferred that the substrate be centrally encompassed at all times, while in the bath, by a helical-shaped anode having a coil diameter of approximately one inch and composed of an electrically conductive wire of approximately 50 mils in diameter.

The choice of anode material may not be arbitrarily made; however, molybdenum, tungsten, iron-nickel, and iron-nickel-molybdenum anodes may successfully be used provided any sludge formations originating at the anode do not enter the bath solution. One of the important factors associated with the choice of anode material, is oxidation in the system. Consequently, inert anodes such as platinum, or the like, may be used provided they do not a lead to excessive system oxidation. It has been found that with the use of either of plating baths #1 or #3, molybdenum anodes are preferred as they do not have to be bagged" and tend to replenish and/ or supply the bath with molybdenum ions; with the use of plating bath #2, a tungsten anode is preferred. Even when a molybdenum anode is used with bath #1, it may be necessary to continually add molybdate solution to the bath in order to maintain the concentration thereof constant at the desired value. It is believed that the ferrous and ferric ions are present in the bulk of the bath solution as a soluble anionic complex, and it is further believed that the ferrous to ferric ionic ratio is of primary concern as to the composition and production of preferred direction of orientation "to each of the baths to maintain the concentrations thereof constant at their respective values during the entire plating process.

The current density involved in the deposition process is not critical and may range, for example, from 25 0 to 1,000, preferably 500, amperes per square foot of carrier surface area exposed in baths #1 and #3 and from 50 to 500, preferably 380, amperes per square foot of carrier surface area exposed in bath #2. The current density primarily determines the rate of deposition of the metallic ions onto the cathode and also affects the rate of diffusion into the cathode film which influences the amount of depositing species which must be in equilibrium with'the reservoir complexes. Consequently, the bathconstituents and current density of the process must be compatible, and the current density may not be arbitrarily chosen. As the current density is one of the prime factors which de- 6 Therefore, it is seen that in accordance with the pres ent invention, there has been devised a new and improved ferromagnetic data storage element whcih is capable of being economically fabricated from ternary altermine the structure of the deposit, it is generally neces- 5 loys of iron and nickel with either molybdenum or sary to modify the plating system to permit the use of a tungsten and which possess a skewed easy direction of specific current density. magnetization characteristic, with respect to the longi- On emergence from the plating bath, the ferromagnetic tudinal axis thereof, without the need for mechanically element is rinsed and dried and is then ready to be inimparted torsional strain either before, during, or after corporated into the electrical circuitry of present-day elec- 10 the deposition process. Additionally, such a device has tronic computers and data processors and operated as a greatly improved magnetic and other properties than coincident current memory element in the same manner heretofore possible and is readily adaptable to be incoras the previously described twistor type of magnetic porated into the electrical circuitry of present day elecdata storage devices and as diagrammatically illustrated in tronic computers and data processors with a minimum Figs. 5 and 6. expenditure of time and effort.

Listed below in chart form, are the electrical opera- While particular embodiments of the invention have tional characteristics of such storage devices in accordbeen shown and described, it will be obvious to those ance with the present invention which were fabricated by skilled in the art of electrodeposition of ferromagnetic the just described electrodeposition process which utilized materials, that changes and modifications may be made each of the electrolytic baths #1, #2, and #3 having prewithout departing from the invention in its broader asferred constituent concentrations as previously shown. In pects,- and therefore, the aim in the appended claims is the chart (Ir) represents the half-select current impulse to cover all such changes and modifications as fall withapplied across the ends of the ferromagnetic element durin the true spirit and scope of the invention. ing storage of the function, via terminals 23 and 2.4 (Fig. What is claimed is: 5); (Is) represents the half-select current impulse ap- 25 l.v A magnetic data storage device comprising an elonplied across the ends of a selected one of coils 25 during gated electrically conductive substrate and a ferromagstorage of the function, coils 25 each being circumferennetic electrodeposit disposed on the surface of said subtially wound about the ferromagnetic element and spaced strate, said electrodeposit being substantially free from apart in the same manner and for the same purposes as mechanically imparted torsional strain and having a preheretofore described; (Is) represents the full-select curferred direction of crystal orientation which produces a rent impulse applied across the ends of a selected one of skewed easy direction of magnetization of said electrocoils 25 via terminals 26-27 during reading of the funcdeposit with respect to the longitudinal axis of said subtion; (uVl) represents the instantaneous readout potenstrate. tial appearing across the ends of the ferromagnetic ele- 2. A magnetic data storage device comprising an elonment at terminals 23-24 indicative of any reversal of the gated electrically conductive core and a ferromagnetic magnetic remanence of the element, i.e. due to pervious electrodeposit disposed on the surface of said core, said binary 1 storage; and (uVl/dVz) represents the operaelectrodeposit being substantially free from mechanicaltional signal to noise ratio of the storage element. 1y imparted torsional strain and having a preferred di- Bath #1 Bath #2 Bath #3 Ir 1901113. 68ma 2501na 170ma. Ia- 44 ma 0 ma 92 ma 6 ma. Is 300 ma 300 ma 5001na 5001119.. uV1 300mv 110mv 30mv mm uVl/d 20 an a 50. No. Turns of coil 40 40 an 20. Wire size of coil #36 #36 #36 #36. Wire size of ele 9 mils 3 m 9 mils 9 mils. Amount oftwist None None None None. Switching time .3;tsec. .3 sec. .3 1sec.-." .3IJSBC. Ooercivity 5 oersteds- 5 oersteds- 6 oersteds. 5 oersteds. Hysteresis squarene Approx. .99- Approx. .99. Approx. .99. Approx. .99.

With reference to Figs. 1 and 3 of the drawings, it is rection of crystal orientation which produces an inclined seen that the ferromagnetic deposit on prior untwisted easy direction of magnetization of said electrodeposit twistor type of storage devices, such as disclosed in pre- With respect to the longitudinal axis of said core. viously referred-to co-pending application 696,987, ap- 3. A magnetic data storage device comprising an pears to have no substantial preferred orientation. This elongated electrically conductive subtrate and a ferrois indicated first of all by the random distribution of fermagnetic electrodeposit disposed on the surface of said romagnetic botryoids 10 as seen in Fig. 1 and by the consubstrate, said electrodeposit being substantially free tinuous nature of the second diifraction ring 11 in Fig. 3, from mechanically imparted torsional strain and having the first discontinuous diffraction ring 12 indicating the a preferred direction of crystal orientation yielding a preferred orientation of the substrate. helical-shaped easy direction of magnetization of said As seen in Figs. 2 and 4, the ferromagnetic deposits on electrodeposit with respect to the longitudinal axis of the storage devices of the present invention, appear to said substrate. have a substantial preferred orientation iS believed 4, A magnetic (la-ta storage device comprising an 101 azccoullt 9 T f magnetic Properties P $11911 gated electrically conductive substrate and a ferromag- T1115 15 mdlcat?d first an by the f netic electrodeposit concentrically disposed on the surrmbutlon of ferrqmagqefic botryolds 13 as Seen m 2 face of said substrate, said electrodeposit being substanal.so by h dlsicommuous of i 3? l tially free from mechanically imparted torsional strain the first dlsciontmilous lfiractlon and having a preferred direction of crystal orientation .nng 15 indicating the preferred orientation of the substraw which produces a skewed easy direction of magnet-Iza- In each instance, the black area 16 at the bottom of the diffraction photos in Figs. 3 and 4 is the shadow cast by the sample holder. The central blackened area 17 in each figure is the portion of the film exposed to the direct X-ray beam.

tion of said electrodeposit with respect to the longitudinal axis of said substrate.

5. A magnetic data storage device comprising: an elongated electrically conductive substrate having a hol- 15 low formed therethrough along the longitudinal axis thereof; and a ferromagnetic electrodeposit disposed on the surface of said substrate, said 'electrodeposit being substantially free from mechanically imparted torsional strain and having a preferred direction of crystal orientation which produces a skewed easy direction" of magnetization of said electrodeposit with respect to said longitudinal axis.

6. A magnetic data storage device comprising a substantially cylindrical shaped electrically conductive sub strate and a ferromagnetic electrodeposit disposed on the surface of said substrate, said electrodeposit being substantially free from mechanically imparted torsional strain and having a preferred direction of crystal orientation which produces a skewed easy direction of magnetization of said electrodeposit with respect to the axis of said substrate.

7, A magnetic data storage device comprising an elongated electrically conductive substrate and a ferromagnetic iron-nickel-molybdenurn electrodeposit disposed on the surface of said substrate, said eleetrodeposit being substantially free from mechanically imparted torsional strain and having a preferred direction of crystal orientation which produces a skewed easy direction of magnetization of said electrodeposit with respect to the longitudinal axis of said substrate.

8. A magnetic binary data storage device comprising an electrically conductive wire core and a ferromagnetic iron-nickel-molybdenum electrodeposit concentrically disposed on the surface of said core, said electrodeposit being substantially free from mechanically imparted torsional strain and having a preferred direction of crystal orientation which produces a helical-shaped easy direction of magnetization of said electrodeposit with respect to the longitudinal axis of said core.

9. A magnetic data storage device in accordance with claim 1 in which said device is encompassed by a plurality of similar electrically energizable coils spaced sdie-by-side with respect to one another.

10. A magnetic data storage device in accordance with claim 6 having a plurality of electrical conductors threaded therethrough.

11. A magnetic data storage device comprising an elongated electrically conductive substrate and a ferromagnetic electrodeposit on said substrate, said electrodeposit being substantially free from mechanically imparted torsional strain and having a skewed easy direction of magnetization with respect to the longitudinal axis of said substrate.

12. A magnetic data storage device comprising an elongated electrically conductive substrate and a ferro magnetic electrodeposit =on substantially the entire 'surface area of said substrate, said electrodeposit being substantially free from mechanically imparted torsional strain and having a skewed easy direction of magnetization with respect to the longitudinal axis of said substrate.

13. A magnetic data storage device comprising an elongated electrically conductive substrate and a ferromagnetic electrodeposit on said substrate, said electrodeposit being substantially free from mechanically imparted torsional strain and having a skewed easy'direction of magnetization with respect to the longitudinal axis of said substrate and a preferred direction of crystal orientation.

References Cited in the file of this patent UNITED STATES PATENTS Frey et -al Mar. 22, 1938 Hespenheide Apr. 19, 1955 

